1. Field of the Invention
This invention pertains to a knob for control elements, more particularly, to a knob which is attached to a rotary shaft of a variable control element to provide a plurality of discrete, different, tactile signals to the operator, including discrete points of resistance to rotation of the shaft.
2. Description of the Prior Art
There are many designs patented for tactile feedback of shaft position provided by mechanisms within control elements including switches. Having the tactile feedback mechanism in a knob, however, simplifies the construction of a control element, reduces inventory and permits selection from a wider choice of control elements on the market in constructing a control system.
U.S. Pat. No. 3,662,618, patented by Kroll et al, May 16, 1972, describes a rotary instrument knob which contains a tactile feedback mechanism.
The knob is attached to the shaft of the instrument by a collet that fits symmetrically about the top of the shaft. A termination socket or bushing, which extends through the panel of the apparatus containing the instrument, has a circular groove at the bottom for attaching a fastener behind the panel. The bushing may also include an indexing finger through the panel or may be fastened to the apparatus by gluing or screwing in order to keep it from turning.
The shaft of the instrument passes upward through the bushing. Mounted on the shaft, above the bushing, is a ring holding balls in equally spaced relation from the shaft which momentarily engage depressions in the top of the bushing, as the ring is rotated by the shaft. Above the ring is a ball retaining disk that is pressed against the balls by a helical compression spring which is permanently concentrical in relation to the shaft. The spring is retained and guided axially, concentrically in relation to the shaft in a circular groove which extends around the shaft.